Introduction to the ClearPEM projects

Joao VarelaLIP, LisbonOn behalf of the ClearPEM Collaboration

Jornadas LIP Universidade do Minho, 7-9 January 2010

The ClearPEM ProjectsHigh performance PET scanner for breast cancer detection. Scanner is in clinical tests.

Other applications to brain imaging and PET animal are being pursued

Projects developed by the ClearPEM consortium, in the framework of Crystal Clear at CERN

IP licensed to PETsys, SA

The ClearPEM scanner

Good spatial resolution ( ~1.5 mm in whole FoV)• Fine crystal segmentation (2x2 mm) • DoI measurement with good resolution (FWHM ~2 mm)

• Dual APD readout of individual crystal pixels

High Sensitivity ( ~ 40 cps/kBq in center FoV)• Long LYSO crystals (20 mm)• Two detector plates with large active area

Reduced Random Background (~30%)• Large flux of single photons (up to 10 MHz)

• Coincidence time resolution of ~4 ns FWHM

The ClearPEM scanner

Two detector plates:

• 6144 LYSO 2x2x20 mm3 crystals

• 12288 APD pixel channels

• Dual readout of crystal pixels for DoI measurement

•160x180 mm2 active area

•Water cooling

•75% of detector channels presently installed

The ClearPEM detector

Pulse Shape•Amplifier rise time: 20ns

•Variation of baseline and pulse shape 1-2%

Noise•Pedestal RMS = 2.2 ADC Counts = 5keV

•ENC = 1300 e- r.m.s.

•Inter-channel dispersion ~ 8%

ASIC Performance

Response to test pulse

Noise measurement

Trigger Performance• Events in coincidence up to 1.5MHz (This involves computation of energy

and time, Compton grouping and transmission to the trigger processor)

• Acquisition rate up to 0.8MHz (This involves readout of the event

dataframe after issuing a trigger)

• Disk storage rate ~ 400MB/s

• High performance useful for fast calibration runs

• Needed for other PET applications

Data Acquisition Performance

Ancillary Systems

Cooling• Water cooling of detector plates at 18 oC

• Stability of temperature ± 0.1 oC

Bias Voltages• Regulation of APD bias voltages on the

detector heads (64 regulation channels)

• Long-term stability of HV ~ 28 mV rms

40 hoursr.m.s. ~28 mV

Energy measurements:

• Average energy resolution at 511 keV for the full scanner is 16.0%

• Dispersion of energy resolution of individual crystals is 8.8%

• Good energy linearity (~ up to few percent)

Energy Resolution

Resolution ~12.5%

137Cs

Na-22 spectra summed for all crystals

Photopeak measurements

Time measurement:

• Photon time is extracted from the pulse samples fitted by the function:

• Coincidence time resolution of the whole scanner is 5.2 ns FWHM

Time Resolution

Resolution ~12.5%

137Cs

Typical pulse sampling

Time difference in coincidence events

All scannercoincidences

50 MHz sampling

Asymmetry distributionsfor different impact points in the crystal

DoI Resolution

Energy in bottom vs top APDs

Depth of interaction measurement

• DoI is measured from light asymmetry in crystal dual readout

• From direct measurement (collimated photons):

DoI resolution ~ 2 mm FWHM for light asymmetry ±40%

• Lu-176 background in crystals is used for DoI calibration in whole scanner

• Average light asymmetry is ±59%

Energy is independent of DoI:

E[keV]=Kabs.(Etop+Krel.Ebottom)

Z[mm]=CDOI.((Etopkrel.Ebottom)/(Etop+krel.Ebottom))

• Photopeak position is independent of DoI (up to few percent)

• Energy resolution does not depend on DoI

Energy Dependence on DoI

Resolution ~12.5%

137Cs

Photopeak position as a function of DoI

Energy resolution as a function of DoI

Energy:• Dispersion of channel gains 15.3%

Depth of interaction (Lu-176 background):• Dispersion of DoI calibration constants 7.8%

Time calibration:• Two pulse shape parameters per channel• Dispersion of time calibration constants 2%

Scanner Calibration

~4600 crystals

Distribution of energy calibrations

Distribution of pulse peak time

~4600 crystals

14

Sensitivity measurement:

• Na-22 source A(22Na) = 2.73 µCi ± 0.3% (101kBq)

• Sensitivity at center of FoV for 10 cm Detector Head opening is 1.0%

(350-700 keV, 20 ns)

• Correction factors:• Incomplete (75%) detector: 1.3• In-detector Comptons: ~2

• Corrected sensitivity: ~2.6%

• Monte Carlo estimation: 3.1%

Count rate scan

Sensitivity (100 mm ): 1.0%

ClearPEM Sensitivity

ClearPEM Spatial Resolution

5 mm

1 mm

Point source imaging• Na-22 point source in a grid with 5mm pitch• Energy window 400-600 keV• Sinograms of 16 source positions are added• Reconstruction with 3D-OSEM / STIR

Spatial resolution• Transaxial 1.2 mm FWHM(corrected for source size ~1mm)

DoI effect• Images without using DoI information show

considerable blurring

With DoI

Without DoI

ClearPEM Image Uniformity

Images of uniform Ge-68 source

• Reconstruction with 4 orientations of the detector plates

• Absorption, scatter and corrections are not applied

• Image artifacts due to detector effects are corrected

•Good image uniformity

Cylinder filled with positron emitter Ge-68

EW=400-700keVTW=4 ns6 iterations 3D-OSEM

Scanner Installation• Hospital IPO, Porto

Phase 1 (present)• Patients indicated for PET/CT (other

disease)• Negative breast exams• Tuning the image reconstruction with

real cases• 11 exams done

Phase 2• Patients with positive indication from

x-rays mammography• Assessment of PEM sensitivity /

specificity • Comparison to mammography and MRI

Clinical Tests Program

ClearPEM scanner at IPO Porto

Initial clinical examsExample of typical exam:• dose 8 mCi• 150 mm detector plate opening• 4 angular orientations• coincidence window ±4 ns• energy window 400-650 keV• fraction of randoms in FoV is 35%

Reconstruction:• 3D-OSEM• randoms, attenuation and scatter

corrections not applied• simple normalization correction • on-going work to reduce statistical noise

Dualmodal PET – US

CERIMED , Hospital Marseille, other partners

Ultra-sound probe with elastography capabilities

Cross-reference system and PET-US image fusion

Construction of second ClearPEM machine is well advanced

ClearPEM and Ultrasound

ClearPEM-Sonic

Detectormodules

Cooling plates

35 cm

60 cm

4.5 cm

Version with DoI

PET Animal

Pre-clinical studies with small and medium size animals

PET/MR insert Texas Institute of Preclinical Studies Application to brain imaging /EPFL

High performance PET

Improvements to Electronics/DAQ• Optical S-link (under test)• ASICv4 (in design)• Intelligent Front End Board (in project)• PET Ring Trigger (hw ready)

PET Time-of-Flight (FWHM ~200 ps)• SiPM and TOF ASIC (collaboration with Torino and CERN)

• SPAD single-photon detectors integrated with TDCs

(collaboration with TUDelft and CERN)

E. Albuquerque1, F. G. Almeida2,13, P. Almeida3, E. Auffray10, J. Barbosa2, A. L. Bastos9, V. Bexiga1, R. Bugalho4, C. Cardoso4, S. Carmona8, J.F. Carneiro2, B. Carriço4, C. S. Ferreira4, N. C. Ferreira5, M.

Ferreira4, M. Frade4, F. Gonçalves1, C. Guerreiro5, P. Lecoq10, C. Leong1, P. Lousã6, P. Machado1, M. V. Martins3, N. Matela3, R. Moura4, J. Neves4, P. Neves6, N. Oliveira3, C. Ortigão4, F. Piedade6, J. F. Pinheiro4, P. Relvas6, A. Rivetti , P. Rodrigues4, I. Rolo4, A. I. Santos8, J. Santos2, M. M. Silva1, S.

Tavernier11, I. C. Teixeira1,9, J. P. Teixeira1,9, J. C. Silva4,10, R. Silva4, A. Trindade4, J. Varela4, 12

 1 INESC-ID, 2 INEGI, 3 IBEB/FCUL, 4 LIP, 5 IBILI/FMUC, 6 INOV, 8 HGO, 9 IPO, 10CERN, 11VUB

The ClearPEM Collaboration

Funded by

CERN